This invention relates generally to thermal protective layers and, more particularly, to a thermal protective layer suitable for protection of heat-sensitive apparatus within a missile or other aircraft against the effects of a nearby source of high intensity thermal energy.
It is known in the art that to protect a structure from a source of high thermal energy, an ablating layer is generally provided to dissipate the incident energy. Ablation is a known phenomenon by which energy incident upon an ablating material is dissipated through vaporization of the material rather than by conversion of the energy into heat. That is, during exposure to the heat energy, the material of the ablating layer is vaporized away, dissipating the incident heat energy by converting the solid material of the ablative layer into a vapor.
Thermally-protective coatings are particularly vital in areas where temperature-sensitive equipment is located in close proximity with heat-generating systems. As an example, in some aircraft, as well as in missiles, it is necessary to provide heat protection for delicate electronic assemblies which are located close to engine exhaust conduits. This protection is typically provided by a thermal insulating coating applied to the cover of the electronics assembly.
One example of a thermally protective layer is described in U.S. Pat. No. 4,431,697, "Laser Hardened Missile Casing Structure," issued Feb. 14, 1984, to E. J. Rolinski et al., for a composite missile casing which includes a pair of thermally protective layers comprising a cork composition layer, such as a cork phenolic which may in alternative configurations comprise carbon phenolic, silica phenolic, carbon nitrile or epoxy novalac coatings. Sandwiched between the pair of thermally protective layers is an adhesively bonded laser hardening barrier. The laser hardening barrier comprises a heavy metal bearing resin impregnated carbon fabric.
In most current applications, the method of applying an ablative material to a surface requiring thermal protection is by vacuum bag molding of a cork sheet to the surface. This process is extremely time consuming, expensive, and requires many hours of additional surface preparation. The molded cork sheet may require machining, sanding or grinding to achieve the desired surface finish. There may also be the need for an environmental top coat to protect the cork against moisture absorption, soiling or mechanical damage. Furthermore, there may exist many complex surface configurations requiring thermally protective layers which do not lend themselves to the vacuum bag molding process.